Electromagnet



Dec. 2, 1924. 1,518,020

0. c. TRAVER ELECTROMAGNET Filed July 26, 1921 [TM/enter! O|i\/er- C. Ti-'a\/er-;, y His Attorney.

Patented Dec. 2, 1924.

UNITED STATES PATENT OFF-ICE.

OLIVER C. TRAVER, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTROMAGNET.

Application filed July 26, 1921. vSeriall No. 487,596.

To all whom it may concern:

Be it known that-I, OLIVER C. TRAVER, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Electromagnets, of which the following is a specification.

My invention relates to improvements in electromagnets and more particularly to the armature and cooperating pole of such magnets and has for an object the prevention of the chattering of the armature when an alternating current is flowing in the magnet winding. A further object of my invention is to reduce the residual magnetism in the armature and pole, the residual magnetism being objectionable in that it prevents the release of the armature with the promptness and certainty essential in an apparatus intended to operate with accuracy and precision.

In a magnetic circuit, the amount of residual magnetism depends in a measure upon the length of the magnetic circuit, and also upon the magnitude of the magnetomotive force at the moment of interruption of the circuit of the magnetizing winding. The extent of the chattering of an armature having a shading coil depends upon the relative magnitude of the primary and secondary fluxes through the polar faces. Where the pole face is provided with non-magnetic means for preventing direct engagement between the armature and pole face to limit the residual magnetism and avoid sticking, the reluctance of the shading coil magnetic circuit is relati 'ely high and there is a tendency for chattering to occur. According to my invention, the magnetic circuit of the shading coil is made of very low reluctance thus assuring an increased flux density and a corresponding decrease of chattering while at "the same time means are provided for effectually preventing sticking.

My invention will be better understood from the following description taken in connection with the accompanying sheet of drawings, and its scope will be pointed out in the appended claims.

Fig. 1 shows, partly in section, an embodiment of my invention in an electromagnet having a plunger armature; Fig. 2 shows a modification of the embodiment of my invention shown in Fig. 1; Fig. 3 shows an embodiment of my invention in an electromagnet having a pivoted armature; and Fig. 4 shows a modification of my inven tion relative to the armature shown in Fig. 3.

Figs. 1 and 2 show, partly in section, an electromagnet embodylng my invention and comprising a magnetic structure 1 adapted to .be energized by current in a winding 2 to move an armature 3 of the plunger type toward a polarprojection 4 of the magnetic structure 1, the armature 3 being provided with a rod 5 of nommagnetic material to transmit its movement for any desired purpose. I

As shown in Fig. 1, the. armature 3 is divided into relatively long and short magnetic portions by a short intermediate section 6 of high reluctance such as any suitable non-magnetic material,- the short portion 7 of the armature being provided with a shadin coil or short-circuited winding 8 dispose within a slotted recess 9 therein. Similarly, the pole piece 4 is divided into ie-l'atively long and short magnetic portions by a short intermediate section 10' of .high reluctance, the short portion 11 constituting the pole face. The short magnetic portion 11 and the non-magnetic section 10 may be secured to the polar projection 4 y any suitable non-magnetic means, such as brass screws 11. The short magnetic portion 7 and non-magnetic section 6 may be secured to the armature 3 by the non-magnetic rod 5 which extends through these members and screws into the armature 3, a reduced section on the. rod forming a shoulder to effectively hold the parts together.

The itotal attractive force or pull between the pole comprising" the members 4, 10 and 11 and the armature comprising the members 3, 6, 7 and 8 depends upon the area and the resultant magnetic flux between the two. The tendency to chatter, however, varies with the secondary flux be tween the members 7 and 11 produced by the short-circuited winding 8. With the members 7 and 11 of magnetic material and in the attracted position, the local magnetic circuit, including the members 7 and 11 has a low reluctance and therefore a correspondingly high magneticflux which effectually prevents chattering. Inasmuch as the non-magnetic sections 6 and 10 render the axial lengihs I netic section 19, the short ma bers 7 and 11 sma n comparison with their diameters, the residual magnetism is correspondin -ly small and there is substantiallv no ten ency to stick as compared with that observed in long magnets, particularly when the current in the energizing winding is interrupted at the peak of the wave.

11 the modification of my invention shown in Fig. 2, the armature 3 only is divided into relatively long and short magnetic portions by an intermediate section 6 of non-magnetic material the short portion 12 constituting the pole face of the armature, and the polar projection 4 is provided with a shading coil 13 disposed within a slotted recess 14 therein. As before, with the armature in the attracted position, the local magnetic circuit of the shading coil 13 has a low reluctance and therefore a high secondary flux thus substantially eliminating the tendency to chatter and the length of the members in contact being small in comparison with their diameters, the effect of any residual magnetism is reduced to a minimum thereby insuring a positive release upon interruption of the current in the winding 2, particularly if the current is broken at the peak of the wave.

In Fig. 3, I have shown a modification of my invention embodied in an electromagnet comprising a magnetic structure 15 arranged to be energized by current in a Winding 16 to attract a pivoted armature 17 to wards a polar projection 18 of the magnetic structure 15. The armature 17 is divided into relatively long and short magnetic portions by a transversely disposed non-magetic portion 20 constituting the pole ace of the armature, or as shown in Fig. 4, the armature 17 may be divided into relatively long and short portions by a reluctance comprising the non-magnetic section 19, longitudinally disposed relatively to the armature and an air gap 21 between the short magnetic portion 20 of the armature 17 and the main body thereof. As shown in Fig. 3, the nonmagnetic section 19 and the short magnetic portion 20 may be secured to the armature by plates 17 of non-magnetic material fastened thereto in any suitable manner. The polar projection 18 of the magnetic structure 15 is provided with a non-magnetic section 22, which divides the magnetic member 15 into relatively long and short magnetic portions, the short portion 23 constituting the pole face of the polar projection 18 and being provided with a shading coil 24. The local magnetic circuit including the short magnetic portions 20 and 23 with these members in contact, that is an iron-to-iron contact, provides therefore a low reluctance path for of the magnetic. memthe secondary flux of the shading coil 24 and consequentl the tendency to chatter is substantially eliminated. Furthermore the tendency for the parts to stick upon deenergization of the winding 16 is substantially eliminated, even though there is an iron-to-iron contact, by the non-magnetic sections 19 and 22 which reduce the residual magnetism of the principal magnetic circuit.

lVith alternating current electromagncts constructed in accordance with myinvention, it is therefore possible to have a direct contact of magnetic members which renders the shading coil more effective to prevent. chattering and, even though the current in the principal winding is interrupted at the peak of the wave,.the residual magnetism is so reduced as to insure a positive release of theaarmature to its un attracted position with the promptness and certainty desired.

What I claim as new and desire to secure by Letters Patent of the United States, 1s,

1. An alternating current electromagnet comprising an energizing winding, relatively movable magnetic members, a shading coil on one of said members and a short intermediate section of non-magnetic material dividing-one of said magnetic members into relatively long and short magnetic portions, said short portion constituting the pole of said member whereby in the attracted position of said magnetic menibers chattering is effectively avoided a the residual magnetism tending to hold said magnetic members together upon deenergization of said winding is reduced.

2. An alternating current electromagnetic comprising relatively movable magnetic members and a shading coil on one of said members characterized by the fact that one of said magnetic members is provided with means located near the end thereof for increasing the reluctance of jthe magnetic circuit comprising both of said magnetitmembers and by the fact that the ends of. said. magnetic members engage each other when the magnet is energized to provide a path. of low magnetic reluctance for the flux of the shading coil, whereby chattering is effectively avoided and whereby the residnal magnetism tending to hold the magnetic members together upon deenergization of the magnet is reduced.

3. An alternating current electromagnct comprising a magnetic member adapted to be fixed in said magnet and a relatively movable magnetic member adapted to be v drawn into engagement with said fixed magnetic member upon energization of the magnet, a shading coil mounted in the face of one of said magnetic members and nonmagnetic means arranged to divide one of said members to limit the residual magnetism and provide a local magnetic path for the flux of said shading coil.

4. An alternating current electromagnet comprising an energizing winding, relatively movable magnetic members, and a shading coil in the pole face of one of said members characterized by the fact that one of said members is provided with a short intermediate section of high magnetic relucttance adjacent the pole face thereof dividing said member into relatively long and short magnetic portions whereby in the attracted position of said members a direct contact between magnetic portions thereof is obtained to provide a path of low reluctance for the flux of the shading coil and the residual magnetism tending to hold said members in the attracted position when the winding is deenergized is reduced,

5. An alternating current electromagnet comprising an energizing winding, relatively movable magneticmembers, a shading coil in the pole face of one of said members, and a short intermediate section of high magnetic reluctance in each of said members dividing the same into relatively long and short magnetic portions, the construction and arrangement of parts being such that in the attracted position of said members the short magnetic portions thereof are in contact thus providing a path of low reluctance for the flux of the shading coil and limiting the residual magnetism tending to hold said members in the attracted position when the winding is de energized.

In witness whereof, I havev hereunto set my hand this 21st day of July, 1921.

ULI VER C. TRAVER. 

